1. Field of the Invention
This invention relates to a switch device arranged to switchingly select a desired signal out of a plurality of input signals by using a plurality of analog switches, and more particularly it pertains to a switch device equipped with muting function for preventing pop noise from occurring during switching operation thereof.
2. Description of the Prior Art
To switchingly select a desired signal out of a plurality of input signals, a switch circuit has heretofore been employed which includes a pluraly of analog switches which typically comprise active elements such as transistors. Each such analog switch has an input terminal, an output terminal and a control terminal, and arranged to be turned on in response to a control signal supplied from a control circuit to the control terminal thereof so that an input signal applied to the input terminal is permitted to appear at the output terminal.
In the conventional switch circuit, the analog switches have their output terminals connected together to constitute a common output terminal, and when the control signal is selectively supplied to the control terminal of one of the analog switches while input signals are being applied to the input terminals of the analog switches, only said one analog switch is turned on in response to the control signal so that the input signal being applied to the input terminal thereof is permitted to pass therethrough to the common output terminal.
In order to switch the above-mentioned state to a state in which another input signal being applied to the input terminal of another analog switch is permitted to appear at the common output terminal, the application of the control singal to the first analog switch is interrupted and thereupon a control signal is now applied to the second analog switch, whereby the first analog switch, which has been in the "on" state, is turned off and the second analog switch is turned on, so that the input signal being applied to the second analog switch is now obtained at the common out terminal.
However, the aforementioned conventional switch circuit is disadvantageous in that when it is switched from the state in which a first input signal is available at the common output terminal through a first analog switch to the state in which a second input signal is available at the common output terminal through a second analog switch, the first input signal is suddenly interrupted while the second input signal is suddenly caused to appear, so that an abrupt potential change is caused which results in pop noise. Moreover, there is the tendency that crosstalk and/or interference is caused between the paths for the first and second input signals.